Vibration resistant fasteners

ABSTRACT

A self-locking fastener having a bearing surface comprising a plurality of sets of serrations arranged to penetrate a workpiece such that while a resistance to the loosening of the fastener from the workpiece is created the marring of the workpiece surface is minimized. Use of the fastener is particularly advantageous if the workpiece consists of soft materials such as cast-aluminum or non-heat treated carbon steels. Each set of serration, when viewed as a profile, includes a downwardly inclined surface, a relatively deeper serration and a relatively shallower intermediate serration. The intermediate serration controls the depth of the penetration into a workpiece.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of application Ser. No. 680,212,filed Dec. 10, 1984, now U.S. Pat. No. 4,657,459.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates to self-locking fasteners and, inparticular, to bolts, nuts, washers and the like having serrated bearingsurfaces that provide resistance against the fastener becoming loosenedunintentionally after it has been seated. The self-locking fastener ofthe present invention can be used to particular advantage for workpieceshaving relatively soft bearing surfaces whereby marring of the workpiecesurface is minimized.

2. Description of the Prior Art

A serious problem in joints secured together by threaded members is thepossibility of joint separation due to a nut backing-off from a bolt ora bolt backing-out from a nut or other internally threaded member.Generally, this result can occur when the joint is subjected tovibrations.

Various proposals have been suggested in the past to either eliminate orgreatly reduce the unintentional loosening of threaded members. Becauseof the wide variety of applications in which this undesirable result canoccur, many different types of locking devices have been developed. Oneapproach has been to treat the bearing surface of the fastener in such amanner that the resistance to relative rotation between the fastener anda workpiece in which the fastener is installed is greater than theresistance to relative movement between the mating threads. As a result,the resistance to rotation between the mating threaded parts no longeris the critical factor in determining whether the threaded parts willturn relative to each other.

One important requirement of these fasteners is that the "off" torque(torque required to loosen a tightened fastener) be greater than the"on" torque (torque required to seat a fastener properly.)

Because the bearing surface of these fasteners, for the most part, areserrated or are provided with teeth or the like which are arranged todig into the workpiece to create resistance to relative rotation betweenthe fastener and the workpiece, some damage or marring of the workpiecebearing surface will occur as these fasteners are seated and removed.Such damage to the workpiece causes it to weaken. Hence, a secondimportant requirement of these fasteners is that the effect of marringor damage to the workpiece is minimized.

Generally, most prior art fasteners provided with a lockingcharacteristic in the bearing surface fail to satisfy concurrently theseand other requirements. Those fasteners available at the present timehaving improved "off" torque to "on" torque ratios dig into theworkpiece in such a manner or to such an extent as to weaken greatly theworkpiece. "Notch" effect (the build up of stress concentrations) is acommon result and may cause fatigue failure of the clamped parts. Thisproblem becomes more acute as the thickness of the workpiece is reduced.Those fasteners available at the present time having reduced adverseeffect on the workpiece provide insufficient "off" torque.

The drawbacks of this type of prior art fastener are overcome in afastener such as that disclosed in commonly assigned in U.S. Pat. No.3,605,845. This patent discloses a self-locking fastener which providesa resistance to unintended rotation between the fastener and theworkpiece and yet causes a minimum amount of marring of the workpiecesurface with which the fastener bearing surface is in contact. This isaccomplished by providing a smooth surface annular ring about aplurality of radially disposed serrations which, upon engagement withthe workpiece, opposes further penetration of the serrations andcontrols and extent of penetration of the serrations.

A similar improved fastener is also disclosed in commonly assigned U.S.Pat. No. 3,825,051. This patent discloses a self-locking fastener havinga polygon shaped workpiece bearing surface, such as a hex-head, wherethe serrated segment is formed within an annular segment so thatcircumferentially discontinuous smooth-faced outer bearing surfaces areformed across adjacent flats of the polygon configuration.

Thus, it is an object of the present invention to provide a new andimproved self-locking fastener having a locking mechanism included inthe bearing surface of the fastener and which is also provided with astress regulating configuration within the locking mechanism to controlthe extent of penetration of the fastener into the workpiece.

It is another object of the present invention to provide a self-lockingfastener of this type which provides improved resistance to unintendedrotation between the fastener and a workpiece and yet causes a minimumamount of marring of the workpiece surface with which it is in contact.

It is a further object of the present invention to provide aself-locking fastener which is relatively simple in construction andinexpensive to fabricate.

SUMMARY OF THE INVENTION

The self-locking fastener of the present invention has a bearing surfacewith a plurality of serrations. The serrations, when viewed along acylinder concentric with the longitudinal axis of the fastener, have theappearance of teeth. Between two teeth are a plurality of intermediatesurfaces. The level of the intermediate surfaces, relative to the teeth,is between the crest and root of the teeth. In one preferred embodimenteach section comprises an inclined plane starting at the crest of atooth and proceeding downwardly in the direction of tightening to anintermediate level forming the intermediate surface, which can beconsidered generally parallel to the bearing surface, and then a secondinclined plane extending downwardly in the direction of tightening fromthe intermediate, surface to the root of the tooth. the intermediatesurface reduces the marring of the workpiece by the teeth, yetsufficient resistance to vibration exists to prevent unintentionalloosening of the fastener.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 provides a perspective view of a self-locking bolt constructed inaccordance with the present invention.

FIG. 2 provides an enlarged portion of the perspective view of theself-locking bolt shown in Figure 1.

FIG. 3 provides an enlarged portion of a cross sectional view of oneembodiment of the plurality of serrations between two teeth of theself-locking bolt of FIGS. 1 and 2.

FIG. 4 provides an enlarged portion of a cross sectional view of anotherembodiment of the plurality of serrations between two teeth. Both FIGS.3 and 4 show an intermediate surface which minimizes any marring damage.

FIG. 5 provides a perspective view of a self-locking nut constructed inaccordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The aforementioned objects and other objects of the present inventionwill be more fully understood after consideration of the followingdescription taken in connection with the accompanying drawings.

Referring to FIG. 1, a self-locking bolt constructed in accordance withthe present invention includes a threaded shank 10, and a bolt head 11at one end of shank 10. Bolt head 11 has a bearing flange 12. Thebearing surface of flange 12, that is the surface to be placed inbearing contact against a workpiece (not shown), is provided with aplurality of outwardly disposed serrations 13. In this embodiment theserrations form sets of preferably two, for example serrations 14, whichare parallel to each other leaving a wedge-shaped portion, for example15, between the sets. Serration sets are defined as the surfacesrepresented in FIG. 1 by four parallel lines.

In another embodiment (not shown) the bearing surface of flange 12 mayinclude a plurality of radially disposed serrations rather than theparallel serration sets 14.

Referring to FIG. 2, which is an enlarged portion of the perspectiveview of the self-locking bolt shown in FIG. 1, the bolt head 11 isformed at one end of threaded shank 10 and includes bearing flange 12and the direction of tightening is indicated by the arrow. The bearingsurface of flange 12 has, in this embodiment, outwardly disposedserrations. When viewed along a cylinder concentric with thelongitudinal axis of the fastener, the crest of a tooth is representedby 16. A downwardly inclined surface 17 starts at crest 16 and ends atone end of an intermediate parallel surface 18. Surface 18 can beconsidered generally parallel to the bearing surface of flange 12 or thenon-bearing top surface 19 of flange 12. A second downwardly inclinedsurface 20 starts at the oher end of parallel surface 18 and extendsdownwardly in the direction of tightening to a root 21 of the nexttooth. Root 21 of the next tooth is connected by a wall 22, which isgenerally parallel to the longitudinal axis fo the bolt, to the crest 24of that tooth. Because the serrations in this embodiment are parallel toeach other, a pie-shaped wedge 23 separates successive parallel sets.Three pie-shaped wedges 23 are shown to illustrate this feature of thefirst embodiment. Each pie-shaped wedge 23 is at the same plane as root21. Although wall 22 can generally be considered to be 90° to the planeof the bearing surface, variations from 90° are acceptable.

FIG. 3 is an enlarged cross sectional view of one set of serrationsshown in FIG. 2. From the crest 16 of the tooth, downwardly inclinedsurface 17 proceeds in the direction of tightening to one end ofintermediate parallel surface 18. As previously described, the surface18 is generally parallel to bearing flange 12. The surface 18 is at ashallower depth, compared to crests 16 or 24, than the greater depth ofroot 21. From the other end of intermediate parallel surface 18, aninclined surface 20 extends downwardly in the tightening direction toroot 21 of the adjacent tooth. The wall 22 extends from the root 21 tothe crest 24 of the adjacent tooth. The surfaces 17, 18, 20, 21 and 22along with the crest 16 can be considered as one set of serrations. Whenviewed at a right angle to the surface 18, the set consists of fourparallel lines.

FIG. 3 also shows another feature of the present embodiment of theinvention. The root 21 is connected to the wall by a radius or fillet25, which is not considered essential to the present invention. Thecrests 16 and 24 are also preferably radiused rather than having sharpedges.

FIG. 4 is an enlarged cross sectional view of one set of serrations ofanother embodiment of the invention. The embodiment of FIG. 4 differsfrom the one shown in FIG. 3 in that the crests 26 and 27 of the teethare truncated with small flats. A downwardly inclined surface 28 startsat a truncated crest 26 and extends in the direction of tightening toone end of an intermediate surface 29 that is generally parallel to thebearing surface of flange 12. The intermediate surface 29 is at a levelbetween that of crest 26 and a root 31. Another downwardly inclinedsurface 32 begins at the other end of surface 29 and extends in thedirection of tightening the root 31. Surfaces 26, 28, 29, 31, 32 and 33can be considered as one set of serrations in this embodiment. Alsoshown in FIG. 4 is a fillet 34 which connects a root 31 with a wall 33that is generally perpendicular to the surface of flange 12. Fillet 34,however, is not considered essential to this embodiment of theinvention.

FIG. 5 shows the invention described above in the form of a nut 40.

FIG. 6 shows the invention described above in the form of a washer 50.

In general, the present invention provides means for limiting thefastener's serrations from penetrating too deeply into the matingsurface of the workpiece (not shown) while still providing "off" torqueswhich are greater than "on" torques. This control is provided by theintermediate shallower parallel surfaces (for example 18 in FIG. 3, and29 in FIG. 4). As the fastener is seated, the crests 16, 26 of theserrations engage the mating surface of the workpiece (not shown) andbegin to penetrate the workpiece. Penetration continues until parallelsurfaces 18, 29 contact the mating surface of the workpiece. At thispoint the total bearing area in contact at the mating surface will besufficient to resist further penetration.

Parallel surfaces 18, 29 can be considered intermediate surfaces whichare closer in the axial direction of the fastener to the non-bearingsurface 19 of the bolt than are the crests of the teeth and which arefurther in the axial direction of the fastener from the non-bearingsurface of the bolt than are the roots of the teeth. As a result of therelative location of the intermediate surfaces, the teeth are adapted topenetrate into a mating workpiece surface in which the bolt is beinginstalled, and the intermediate surfaces are adapted to control andlimit the extent of penetration of the teeth into the workpiece surfacewhen the fastener is operationally installed with the roots of the teethnot bearing against the workpiece surface.

In particular the fasteners of the present invention are more suitablefor use on workpieces consisting of soft material such as cast-aluminumor non-heat-treated carbon steel.

While the serrations have been disclosed and described as originatingfrom the same point on the longitudinal axis of the fastener, or asbeing parallel to each other in sets with each set being separated by apie-shaped wedge, it is to be expressly understood that differentorientations for the disclosed serrations of present invention may alsobe employed with equally beneficial results.

What is claimed is:
 1. A self-locking fastener having a predetermineddirection of tightening and a bearing surface, said bearing surfacecomprising:a plurality of serrations in the form of teeth when viewedalong a cylinder concentric with the longitudinal axis of the fastener,each of said teeth having a root and a crest such that said roots ofsaid teeth generally form a first plane and said crests of said teethgenerally form a second plane; a plurality of walls, each wall extendingfrom the crest of each said tooth to the root of said tooth; and aplurality of intermediate surfaces each being disposed between two ofsaid teeth; said intermediate surfaces being generally disposed betweensaid first and second planes; a plurality of first inclined surfaceseach extending from one of said crests in the direction of tightening toone of said first intermediate surfaces, such that said teeth areadapted to penetrate into a workpiece surface in which said self-lockingfastener is being installed and said first intermediate surfaces areadapted to control and limit the extent of penetration of said teethinto the workpiece surface when said self-locking fastener isoperatively installed and said roots of said teeth do not bear againstsaid workpiece surface; and a plurality of second inclined surfaces eachextending in the direction of tightening from one of said intermediatesurfaces to one of said roots.
 2. The self-locking fastener of claim 1wherein each of said intermediate surfaces is generally parallel to saidfirst and second planes.
 3. The self-locking fastener of claim 1 whereinsaid crests are selected from a group consisting of radiused crests andtruncated crests.
 4. The self-locking fastener of claim 1 wherein saidcrests of said teeth each define a straight radial line originating fromthe same point on the longitudinal axis of the fastener.
 5. Theself-locking fastener of claim 1 wherein said serrations are parallel toeach other in sets and each set is separated by a pie-shaped wedge. 6.The self-locking fastener of claim 5 wherein each said pie-shaped wedgeis disposed generally within said first plane.
 7. The self-lockingfastener of claim 1 wherein said fastener is a bolt.
 8. The self-lockingfastener of claim 1 wherein said fastener is a nut.
 9. The self-lockingfastener of claim 1 wherein said fastener is a washer.
 10. Aself-locking fastener having a predetermined direction of tightening,and a bearing surface, said bearing surface comprising:a plurality ofserrations in the form of teeth when viewed along a cylinder concentricwith the longitudinal axis of the fastener, each of said teeth having aroot and a crest such that said roots of said teeth generally form afirst plane and said crests of said teeth generally form a second planeeach of said plurality of serrations further comprising: a wallextending from the crest of said tooth to the root of said tooth; anintermediate surface disposed between said crest and said root of saidtooth; said intermediate surface being generally disposed between saidfirst and second planes; and a first inclined surface extending fromsaid crest in the direction of tightening to said intermediate surface,such that said tooth is adapted to penetrate into a workpiece surface inwhich said self-locking fastener is being installed and saidintermediate surface is adapted to control and limit the extent ofpenetration of said tooth into the workpiece surface when saidself-locking fastener is operatively installed and said root of saidtooth does not bear against said workpiece surface.
 11. The self-lockingfastener of claim 10 wherein each of said intermediate surfaces isgenerally parallel to said first and second planes.
 12. The self-lockingfastener of claim 11 wherein a said bearing surface further comprises aplurality of second inclined surfaces each extending in the direction oftightening from one of said intermediate surfaces to one of said roots.13. The self-locking fastener of claim 10 wherein a said bearing surfacefurther comprises a plurality of second inclined surfaces each extendingin the direction of tightening from one of said intermediate surfaces toone of said roots.
 14. The self-locking fastener of claim 10 whereinsaid crests are selected from a group consisting of radiused crests andtruncated crests.
 15. The self-locking fastener of claim 10 wherein saidcrests of said teeth each define a straight radial line originating fromthe same point on the longitudinal axis of the fastener.
 16. Theself-locking fastener of claim 10 wherein said serrations are parallelto each other in sets and each set is separated by a pie-shaped wedge.17. The self-locking fastener of claim 10 wherein said fastener is abolt.
 18. The self-locking fastener of claim 10 wherein said fastener isa nut.
 19. The self-locking fastener of claim 10 wherein said fasteneris a washer.